1. Field of the Invention
Multifrequency antennas are desirable in a variety of electronic circuitry, for communications and the like. In many instances it may be desirable to receive signals of a first frequency on one antenna and transmit signals of a second frequency on a second antenna and, because of size and weight considerations it is desirable to provide a single antenna which can perform these function. Many other applications may also arise, such as where equipment is constructed to transmit and/or receive on a plurality of different frequencies.
2. Description of the Prior Art
In the prior art, typically dual frequency antennas are extremely complicated or large and cumbersome, so that in either case they are extremly expensive to manufacture and, generally, much too large for many uses. An example of the former type of dual frequency antenna is disclosed in U.S. Pat. No. 2,479,227, entitled "Dual Frequency Antenna", issued to E. N. Gilbert, on Aug. 16, 1949. An example of the latter type of dual frequency antenna is disclosed in U.S. Pat. No. 3,971,032, entitled "Dual Frequency Microstrip Antenna Structure", issued to Robert E. Munson, et al on July 20, 1976.
With the advent of microstrip antennas, such as that described in U.S. Pat. No. 3,803,623, entitled "Microstrip Antenna", and issued to Lincoln H. Charlot, Jr., on Apr. 9, 1974, simple, low profile antennas became available. A comprehensive discussion and analysis of microstrip antennas has been published in the periodical "IEEE Transactions on Antennas and Propagations", Jan. 1975, pages 90-93, entitled Microstrip Antennas, written by John Q. Howell. While the microstrip antennas are simple and inexpensive to construct, any multifrequency antennas utilizing this technology are either severely limited in form or complicated to construct.